1. Field of Invention
The present invention relates to an assembly including a shaft or a portion of shaft mounted rotatably around its axis and of a roller bearing by which it is supported. The present invention applies in particular to the installation of a bearing for a turbine shaft in a gas turbine engine.
2. Description of the Related Art
FIG. 1 represents a partial view of a gas turbine engine 1. The high pressure turbine rotor 2 is situated immediately downstream of the combustion chamber 3 and is driven into rotation by the action of the gases flowing therefrom on the vanes 4 mounted on the disk 5 of the rotor 2. The turbine disk 5 is interconnected with a journal 6, arranged downstream relative to the flow direction of the gases. At the end of the journal 6 a bearing is mounted which supports the rotary assembly. Only the internal ring 8 of the bearing is here represented. The rotor 2 is interconnected upstream with a drum 7 linked with the high pressure compressor, not represented, itself supported rotatably by an upstream bearing. This rotary assembly forming the high pressure spool of the engine is supported by dint of both these bearings either by the fixed structure of the engine in the case of a single spool engine or by another rotary assembly in the case of a double or triple spool engine for independent low pressure or intermediate pressure stages.
In current engines, the internal ring is interconnected with the shaft or journal by sintering. By this operation the ring is clamped on the shaft or journal. The coupling may then resist the rotational torques to which the ring is subjected during the operation of the engine as well as to the axial loads. A downstream nut 9, screwed on the journal and blocked in rotation, locks the ring 8 in position and ensures cohesion of the assembly should the ring become loose on the journal because of, for example, worn contact surfaces or excessive heating of the components. To cover all the faulty cases and avoid any incident the nut may be oversized to be able to impart high tightening torque to the assembly.
This solution exhibits therefore the shortcoming of high mechanical load of the parts. The size of the nut depends in particular on the load requested. It is hence necessary to design and to implement heavy and complex tools with force division means.
Besides, it would be desirable, for certain applications, in particular in the case of new more compact engines, to reduce the axial space requirements of the shaft supporting the turbine, with its bearing. The position of the bearing being itself perfectly defined in its environment relative to the other components of the engine such as the fixed structure, only the section including the nut could be modified. However, taking into account the loads reminded of above, it is not possible to reduce the size of the nut without reducing the mechanical strength of the assembly.
To solve this problem, it has been suggested in a first step to do away with the nut and to weld the ring directly to the shaft. This solution, however, may not be acceptable, at least for certain engines, because of the different materials forming both these components, corrosion problems which might derive therefrom, and of the complex operations when, at a later stage, it would be necessary to intervene on the part itself.